fix: scim user query endpoint don't allow SortBy custom field (#9235)

# Which Problems Are Solved
- scim list users endpoint (`GET /scim/v2/{orgId}/Users`): handle
unsupported `SortBy` columns correctly

# How the Problems Are Solved
- throw an error if sorting by an unsupported column is requested

# Additional Context
Part of #8140

internal/api/scim/integration_test/users_list_test.go

@@ -93,6 +93,14 @@ func TestListUser(t *testing.T) {
 			wantErr:   true,
 			errorType: "invalidValue",
 		},
+		{
+			name: "custom sort field",
+			req: &scim.ListRequest{
+				SortBy: gu.Ptr("externalid"),
+			},
+			wantErr:   true,
+			errorType: "invalidValue",
+		},
 		{
 			name: "unknown filter field",
 			req: &scim.ListRequest{

internal/api/scim/resources/resource_list.go

@@ -118,7 +118,7 @@ func (r *ListRequest) toSearchRequest(defaultSortCol query.Column, fieldPathColu
 	if r.SortBy == "" {
 		// set a default sort to ensure consistent results
 		sr.SortingColumn = defaultSortCol
-	} else if sortCol, err := fieldPathColumnMapping.Resolve(r.SortBy); err != nil {
+	} else if sortCol, err := fieldPathColumnMapping.Resolve(r.SortBy); err != nil || sortCol.FieldType == filter.FieldTypeCustom {
 		return sr, serrors.ThrowInvalidValue(zerrors.ThrowInvalidArgument(err, "SCIM-SRT1", "SortBy field is unknown or not supported"))
 	} else {
 		sr.SortingColumn = sortCol.Column